Maybe it is possible to use an MCPCB as is common for high-performance flashlight LEDs or at least make it possible to directly stick a heat-sink to the back of the LED by putting a hole into the PCB underneath the LED, and re-arranging the ICs around it, if they really have to be on the back of the PCB. The classic fischer elektronik fcool ICK LED R 28 x 15 G would work wonders for a 3W LED.

It would be great to have a high-brightness RGB LED like the Pixie on the market that, once properly heat-sink-able, also no longer requires thermal protection circuitry.